The invention relates to an apparatus for measuring the flow velocity of a fluid, the apparatus including an oscillation generator triggered by a circuit driver and a receiver arranged in oblique opposed relation to the generator with respect to the direction of flow of the fluid, and an analyzing circuit for the determination of the transit time of the oscillations through the fluid.
German OS No. 2 351 290 describes a process wherein two reciprocal ultrasonic transducers, mutually opposed obliquely to the direction of the flow of the fluid, are alternatingly operated as transmitters and receivers and the time between the emission of a signal and the receipt of it is measured.
An arrangement for carrying out this process comprises an analyzing circuit in which a gate circuit is provided which is opened during the transit time of a signal, that is, the time between the emission of the signal and the receipt of it, and thereby establishes a connection between an oscillator and a back-and-forth counter. This back-and-forth counter is reversed in time of the reversal of the reciprocal ultrasonic transducer from forward to backward counters and vice versa. The differential value determined thus in the case of two successive measurements if fed to a storage device and is fed from the storage device in time to the reversal of the counter and of the ultrasonic transducers and via a digital analogue transducer to a display unit.
This known analyzing circuit not only has the disadvantage of a very high expenses regarding the circuit, but also that of an only very limited precision, especially in the case of shorter distances between the ultrasonic transducers. The latter drawback results from the pulse operation of the ultrasonic generators, whereby, because of the unavoidable build-up process, no precisely determinable pulse edges result and thus the point in time of the arrival in the case of the transducer, operated as a receiver, may not be precisely determined, and therefore errors result which, in the case of shorter distances between the ultrasonic transducers, lead to a considerable falsification of the measuring result.
The goal of the invention is to propose an apparatus of the initially mentioned type which is distinguished by a low construction cost and by a high precision.